a) Field of the Invention
The invention is directed to a 360-degree all-around reflector with retroreflectors that are triple prisms, especially for application in geodetic surveying with tachymeters and other geodetic measurement devices.
b) Description of the Related Art
In recent years, 360-degree all-around reflectors have made up a fixed component in electronic tachymeters for tracking reflectors on land. Continuous target tracking is made possible through further automation of the electronic tachymeter and is used to an increasing extent in practice. 360-degree all-around reflectors have also become increasingly important for controlling construction machinery because automation in the positioning of this machinery is also desired.
U.S. Pat. No. 4,875,760 (Youngren) discloses a 360-degree all-around reflector unit with a base body, wherein a quantity of retroreflectors are arranged at the periphery of the base body in such a way that they cover an angular area of 360.degree. in a plane. Accordingly, it is possible to reflect incident light from light sources or target beams of geodetic devices lying in the reflector plane back to the starting point.
U.S. Pat. No. 5,301,435 (Buckley) describes an all-around reflector arrangement comprising prisms which are arranged in two tiers of three prisms each at the periphery of a cylinder, so that they cover an angular area of 360.degree. and incident light, for example, from a target station, is reflected back to the base station. Known triple prisms are used as retroreflectors.
In a 360-degree all-around reflector, it depends in particular on how close to one another the reflectors can be arranged and on the size of the angle of the adjacent reflectors relative to one another in order that the pupils, when symmetrically adjusted, are cut evenly and at most only by half. In this case, the apparent tips of the reflectors lie in a plane; that is, they are not offset with respect to height, so that pointing or sighting can always be carried out visually or also automatically at the same height. If the effective total surface of the pupil changes only slightly, this also results in only slight energy loss and there is therefore also no range loss when measuring distances with tachymeters. The arrangements of Youngren and Buckley do not meet these requirements. The spacing between the individual adjacent reflectors is relatively large.
In an arrangement for retroreflection of a beam with triple mirrors such as is described in DE 195 30 809 (Leica AG), a 360-degree all-around reflector is provided in which the prisms are tightly packed relative to one another, but whose apparent centers are offset with respect to height. The pupils are therefore offset with respect to height resulting in disadvantages for a range finder with a biaxially arranged transmitting and receiving light bundle with respect to positioning accuracy and precision of distance measurement. In order to avoid these disadvantages, the respective prism entrance surface must be aligned more exactly with the target line of the tachymeter at the target point. While this is possible for picking up the measurement point, it entails grave difficulties with respect to controlling construction machinery, for example.